Answer:
Option C. r = ½√P/πI
Explanation:
P = 4πIr²
From the question given above, we are to make r the subject of the formula. This can be achieved as shown below:
P = 4πIr²
Divide both side by 4πI
r² = P/4πI
Take the square root of both side
r = √P/4πI
The square of 4 is 2. Therefore the expression becomes:
r = ½√P/πI